Osseointegration of titanium implants in the tibia. Electron microscopy of biopsies from 4 patients

Titanium with nanotopography attenuates the osteoclast-induced disruption of osteoblast differentiation by regulating histone methylation

The bone remodeling process is crucial for titanium (Ti) osseointegration and involves the crosstalk between osteoclasts and osteoblasts. Considering the high osteogenic potential of Ti with nanotopography (Ti Nano) and that osteoclasts inhibit osteoblast differentiation, we hypothesized that nanotopography attenuate the osteoclast-induced disruption of osteoblast differentiation. Osteoblasts were co-cultured with osteoclasts on Ti Nano and Ti Control and non-co-cultured osteoblasts were used as control. Gene expression analysis using RNAseq showed that osteoclasts downregulated the expression of osteoblast marker genes and upregulated genes related to histone modification and chromatin organization in osteoblasts grown on both Ti surfaces. Osteoclasts also inhibited the mRNA and protein expression of osteoblast markers, and such effect was attenuated by Ti Nano. Also, osteoclasts increased the protein expression of H3K9me2, H3K27me3 and EZH2 in osteoblasts grown on both Ti surfaces. ChIP assay revealed that osteoclasts increased accumulation of H3K27me3 that represses the promoter regions of Runx2 and Alpl in osteoblasts grown on Ti Control, which was reduced by Ti Nano. In conclusion, these data show that despite osteoclast inhibition of osteoblasts grown on both Ti Control and Ti Nano, the nanotopography attenuates the osteoclast-induced disruption of osteoblast differentiation by preventing the increase of H3K27me3 accumulation that represses the promoter regions of some key osteoblast marker genes. These findings highlight the epigenetic mechanisms triggered by nanotopography to protect osteoblasts from the deleterious effects of osteoclasts, which modulate the process of bone remodeling and may benefit the osseointegration of Ti implants.

Osseointegration and current interpretations of the bone-implant interface

Complex physical and chemical interactions take place in the interface between the implant surface and bone. Various descriptions of the ultrastructural arrangement to various implant design features, ranging from solid and macroporous geometries to surface modifications on the micron-, submicron-, and nano- levels, have been put forward. Here, the current knowledge regarding structural organisation of the bone-implant interface is reviewed with a focus on solid devices, mainly metal (or alloy) intended for permanent anchorage in bone. Certain biomaterials that undergo surface and bulk degradation are also considered. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin. In the published literature, as many as eight distinct arrangements of the bone-implant interface ultrastructure have been described. The interpretation is influenced by the in vivo model and species-specific characteristics, healing time point(s), physico-chemical properties of the implant surface, implant geometry, sample preparation route(s) and associated artefacts, analytical technique(s) and their limitations, and non-compromised vs compromised local tissue conditions. The understanding of the ultrastructure of the interface under experimental conditions is rapidly evolving due to the introduction of novel techniques for sample preparation and analysis. Nevertheless, the current understanding of the interface zone in humans in relation to clinical implant performance is still hampered by the shortcomings of clinical methods for resolving the finer details of the bone-implant interface. STATEMENT OF SIGNIFICANCE: Being a hierarchical material by design, the overall strength of bone is governed by composition and structure. Understanding the structure of the bone-implant interface is essential in the development of novel bone repair materials and strategies, and their long-term success. Here, the current knowledge regarding the eventual structural organisation of the bone-implant interface is reviewed, with a focus on solid devices intended for permanent anchorage in bone, and certain biomaterials that undergo surface and bulk degradation. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin.

A Review of the Impact of Implant Biomaterials on Osteocytes

In lamellar bone, a network of highly oriented interconnected osteocytes is organized in concentric layers. Through their cellular processes contained within canaliculi, osteocytes are highly mechanosensitive and locally modulate bone remodeling. We review the recent developments demonstrating the significance of the osteocyte lacuno-canalicular network in bone maintenance around implant biomaterials. Drilling during implant site preparation triggers osteocyte apoptosis, the magnitude of which correlates with drilling speed and heat generation, resulting in extensive remodeling and delayed healing. In peri-implant bone, osteocytes physically communicate with implant surfaces via canaliculi and are responsive to mechanical loading, leading to changes in osteocyte numbers and morphology. Certain implant design features allow peri-implant osteocytes to retain a less aged phenotype, despite highly advanced extracellular matrix maturation. Physicochemical properties of anodically oxidized surfaces stimulate bone formation and remodeling by regulating the expression of RANKL (receptor activator of nuclear factor-κB ligand), RANK, and OPG (osteoprotegerin) from implant-adherent cells. Modulation of certain osteocyte-related molecular signaling mechanisms (e.g., sclerostin blockade) may enhance the biomechanical anchorage of implants. Evaluation of the peri-implant osteocyte lacuno-canalicular network should therefore be a necessary component in future investigations of osseointegration to more completely characterize the biological response to materials for load-bearing applications in dentistry and orthopedics.

Quantitative kinetic analysis of gene expression during human osteoblastic adhesion on orthopaedic materials

Little information was found in the literature about the expression on hydroxyapatite (HA) materials of genes specific of cellular adhesion molecules although more were found on titanium-based substrates. Hence, the goal of this work was to study by a kinetic approach from 30 min to 4 days the adhesion of Saos-2 cells on microporous (mHA) and non-microporous hydroxyapatite (pHA) in comparison to polished titanium. Our strategy associated the visualization of adhesion proteins inside the cells by immunohistochemistry and the quantitative expression of genes at mRNA level by real-time PCR. The cell morphology was assessed using scanning electron microscopy and the number of cells thanks to biochemical techniques. The cellular attachment was the highest on mHA from 30 min to 24 h although the cell growth on mHA was the lowest after 4 days. Generally, the Saos-2 osteoblastic cells morphology on mHA was radically different than on other surfaces with the particularity of the cytoplasmic edge, which appeared un-distinguishable from the surface. The revelation by specific antibodies of proteins of the cytoskeleton (actin) and the focal adhesions (FAK, phosphotyrosine) confirmed that adhesion and spreading were different on the 3 materials. The actin stress fibres were less numerous and shorter on mHA ceramics. Cells had more focal contacts after 4 h on mHA compared to other substrates but less after 24 h. The highest values of total proteins were extracted from mHA at 0.5 and 24 h and from pHA at 1, 4, and 96 h. The alphav and beta1 integrin, actin, FAK, and ERK gene expression were found to be different with adhesion time and with materials. C-jun expression was comparable on mHA, titanium and plastic but was largely higher than on pHA at 0.5 and 1 h. On the contrary, c-fos expression was the highest on pHA after 0.5 h and the lowest after 1h. This difference between c-fos and c-jun expression on pHA after 0.5 h could be related to the fact that these two genes may differ in their signalling pathways. The expression of the alkaline phosphatase gene after 4 days was lower on mHA compared to other materials demonstrating that the microstructure of the mHA ceramic was not favourable to Saos-2 cells differentiation. Finally, it was demonstrated in this study that HA and titanium surfaces influence as well gene expression at early times of adhesion as the synthesis of adhesion proteins but also proliferation and differentiation phases. Indeed, the signal transduction pathways involved in adhesion of Saos-2 cells on HA and titanium were confirmed by the sequential expression of alphav and beta1 integrins, FAK, and ERK genes followed by the expression of c-jun and c-fos genes for proliferation and alkaline phosphatase gene for differentiation.

Erweiterter push out-Test zur Schädigungscharakterisierung der Implantat-Knochen-Grenzfläche / Extended push-out test to characterize the failure of bone-implant interface

To study the mechanical behaviour of the implant-bone interface the push- or pull-out test was overtaken from material science. Most authors equate the maximum load (break point) with the failure of the implant integration. Extending the test procedure by acoustic emission analysis reveals the possibility to detect the failure of the interface more in detail and from its earliest beginning. The development of disconnection between host and implant was found to start long before the ultimate load is reached and can be monitored and quantified during this period. The active interface mechanisms are characterized by the distribution function of acoustic emissions and the number of hits per time defines the kinetics of the failure. From clinical studies a gradual subsidence of loaded implants is known starting long time before the definite implant failure. The presented extension of the push-out test with acoustic emission analysis allows the detection of a critical shear stress tc which demarks the onset of the gradual interface failure. We believe this value to represent the real critical load which should not be exceeded in the clinical application of intraosseous implants.

Behaviour of nitinol in osteoblast-like ROS-17 cell cultures

Nickel titanium shape memory metal alloy Nitinol (NiTi) has been used in dental wares and in gastrointestinal surgery. Nitinol is a promising implant material in orthopedics, but its biocompatibility, especially in long-term implantation is not confirmed yet. We studied Nitinol's effect on a cell culture model. Comparisons to stainless steel, pure titanium and pure nickel were performed. The effects of Nitinol on cell death rate, the apoptosis rate and the formation of local contacts were studied on rat osteosarcoma cell line ROS-17 in 48-h cultures. The cell death rate was assessed with combined calcein-ethidium-homodimer labelling. The amount of dead cells 1000 cells were as follows: four in the NiTi, 21 in the Stst, 4.8 in the Ti and 51 in the Ni group. In the NiTi and Ti groups, the number of dead cells was significantly lower (p < or = 0.01) than in Ni group. The rate of apoptosis was detected with TUNEL-assay. The assay results were: 1.93 apoptotic cells 1000 cells in the NiTi, 1.1 in the Stst, 2.98 in the Ti and 0.62 in the Ni group. A comparison of these two results shows that 48% of the dead cells were apoptotic in the NiTi, 56.6 in the Stst, 62% in the Ti and only 1.8% in the Ni group. The focal contacts were stained with a paxillin antibody and counted. There were marked differences in the number of focal contacts per unit area compared to NiTi (774 focal contacts): 335 in Stst (p < or = 0.01), 462 in Ti (p < or = 0.01) and 261 in Ni (p < or = 0.005). Our results show that NiTi is well tolerated by the osteoblastic type ROS-17 cells.

Biomechanical characterization of osseointegration: an experimental in vivo investigation in the beagle dog

This study reports the results of torsion tests, pull-out tests, and lateral loading tests on osseointegrated commercially pure titanium fixtures. The tests were performed in vivo on six beagle dogs. Three fixtures, each with a diameter of 3.7 mm, were installed bilaterally in the tibia of each animal. The mean maximal pull-out load was 1.55 kN (n = 4), the mean maximal lateral transverse load was 0.21 kN (n = 2), the mean maximal lateral axial load was 0.18 kN (n = 2), the mean breakpoint torque was 0.31 Nm (n = 3), and the mean maximal torque was 0.43 Nm (n = 3). The torsion test revealed an almost immediate plastic deformation of the interface between the implant and bone; this indicates that although the contact between the bone and the implant is close, there is no strong bond, at least not in shear. The major transfer of load from the implant to the surrounding bone tissue must therefore depend on the design of the implant. A histological evaluation with measurements of the amount of bone in contact with the fixtures was performed. By the use of the histological and mechanical data, it is possible to estimate shear stresses in bone tissue (pull-out test) and in the interface (torque test). The mean maximal shear stress in bone tissue in the pull-out tests was 100 MPa (n = 4); the mean shear stress in the interface was 4.3 MPa (n = 3) in the torsion tests at the breakpoint torque and was 6.0 MPa (n = 3) at the maximal torque. It was also possible to estimate the shear modulus of elasticity in the pull-out and torque tests. The mean shear modulus in pull-out was 119 MPa (n = 4), and the mean apparent shear modulus in torsion was 9 kPa (n = 3) for an assumed interface thickness of 100 nm and was 86 kPa (n = 3) for an assumed interface thickness of 1,000 nm.

Biocompatibility of nickel-titanium shape memory metal and its corrosion behavior in human cell cultures

Nickel-titanium alloy (Nitinol) is a metallic biomaterial that has a unique thermal shape memory, superelasticity, and high damping properties. Nitinol is potentially very useful in orthopedic surgery, for example. At present, there are not enough confirmative biocompatibility data available on Nitinol. The aim of our study was to clarify the primary cytotoxicity and corrosion rate of Nitinol in human cell cultures. Comparisons were made with stainless steel (Stst), titanium (Ti), composite material (C), and control cultures with no test discs. Human osteoblasts (OB) and fibroblasts (FB) were incubated for 10 days with test discs of equal size, 6 x 7 mm. The cultures were photographed and the cells counted. Samples from culture media were collected on days 2, 4, 6, and 8, and the analysis of metals in the media was done using flameless atomic absorption spectrophotometry. The proliferation of FB was 108% (Nitinol), 134% (Ti) (p < 0.02), 107% (Stst), and 48% (C)(p < 0.0001) compared to the control cultures. The proliferation of OB was 101% (Nitinol), 100% (Ti), 105% (Stst), and 54% (C) (p < 0.025) compared to the controls. Initially, Nitinol released more nickel (129-87 micrograms/L) into the cell culture media than Stst (7 micrograms/L), but after 2 days the concentrations were about equal (23-5 micrograms/L versus 11-1 micrograms/L). The titanium concentrations from both Nitinol and Ti samples were all < 20 micrograms/L. We conclude that Nitinol has good in vitro biocompatibility with human osteoblasts and fibroblasts. Despite the higher initial nickel dissolution, Nitinol induced no toxic effects, decrease in cell proliferation, or inhibition on the growth of cells in contact with the metal surface.

Advances in the microscopy of osteoarthritis

This review describes recent contributions made by microscopy to the understanding of osteoarthritis, a clinical syndrome the pathological features of which are well defined by classical white light microscopy. The fluorescence and reflected light, conventional and scanning optical microscopy of excised osteoarthritic tissue preparations, from human and animal sources, has enabled the identification of cell proteins such as S100, of matrix components such as the proteoglycans and collagens, and of adhesion molecules including fibronectin, the integrins and tenascin. Comparable microscopic studies have been made of cell and tissue culture preparations of osteoarthritic cartilage and synovium. Scanning optical microscopy also allows the rapid measurement, in hydrated osteoarthritic tissues, of cell density, cell size, surface roughness and other parameters. The importance of water in sustaining the physical attributes of cartilage is accepted and new forms of electron microscopy can play important parts in the study of unfixed osteoarthritic cartilage. These methods include the low temperature scanning electron microscopy and electron probe x-ray microanalysis of hydrated bulk material and the high resolution transmission electron microscopy of low temperature replicas of cartilage surfaces. Understanding of osteoarthritis has been facilitated by these advances and will continue to be enhanced as new techniques of microscopy evolve.

Three-dimensional examination of bone structure around hydroxyapatite implants using digital image processing

This study introduced a new method for three-dimensional (3D) examination of the bone structure around an implant and presented 3D bone-implant contact rates. A block of nondecalcified implant tissue was ground gradually at an interval of 80 micrograms for the collection of serial two-dimensional (2D) images. An image of the stained block surface was instantly recorded by a charge-couple device (CCD) camera and computer-aided system. A 3D model was reconstructed from 60-70 sheets of serial 2D images. The 3D bone structure around the implant was shown in perspective and displayed all sides of the implant. The bone-implant contact rate depended on the cutting position and direction in the specimen. The 3D model will be necessary and valuable for the biomechanical study of dynamic bone changes around implants.

Ultrastructural aspects of the intact titanium implant-bone interface from undecalcified ultrathin sections

An osseointegrated oral implant with surrounding bone was used for electron microscopical analyses of the implant-bone interface. The bulk metal was removed by sawing and grinding techniques, leaving only the plasma-sprayed titanium coating anchored in mineralized bone. Ultrathin sections were realized from these reduced interface areas and underwent ultrastructural and crystallographic assessments. The microscopical observations showed that ultramicrotomy was suitable for producing such interface sections. Two different, concomitant, interfacial structures were noticed. On the one hand it was possible to observe bone crystals directly apposed on the implant surface; on the other, a granular electron-dense substance was interposed between the plasma-sprayed coating and the bone. The applied technical approach allows one to study the osseointegration process, at high resolution levels, of intact interfaces from complete osseointegrated implants.